Iím looking for a new oscilloscop. The old one is more that 30 years things are not really working anymore.

I havenít seen a description anywhere but I got the idea to use FFT to adjust for minimum distortion when feeding an amplifier with a pure sinus wave. Is this possible at all and is it possible with a low-cost scop like this one? Rigol DS1052E

What I want to do is to find the best working point of a tube and best bias and stuff like that.

I have that scope, and the FFT is pretty basic. I believe that the resolution is only 8 bits, leaving it somewhat lacking for this purpose. I purchased a cheap HP distortion meter and use this. I think I read somewhere that you can use the distortion meter output to feed in to scope and use this too to help with distortion reduction.